In geometric construction what does the phrase "lay off" mean?

I have a problem that starts "Construct equilateral triangle ABC. On side AB construct isosceles right triangle ADB with AB as hypotenuse. Lay off EB on BC equal in length to BD" What does the phrase "Lay off" mean in this context. I've never seen it before, but i ume this to mean that EB should be equal in length to BD, but not on the line BC.